Which of these numbers is prime? ${28,\ 33,\ 49,\ 59,\ 95}$
Solution: A prime number has exactly two factors: 1 and itself. The factors of 28 are 1, 2, 4, 7, 14, and 28. The factors of 33 are 1, 3, 11, and 33. The factors of 49 are 1, 7, and 49. The factors of 59 are 1 and 59. The factors of 95 are 1, 5, 19, and 95. Thus, 59 is a prime number.